Talius is a vault dweller from Vault 13, sent out by the Overseer to find a Water Chip. He was captured by super mutants and dipped in the Vats, which led to a rare transformation into a ghoul-like mutant similar to Harold, as opposed to the typical super mutant. He was rescued under ambiguous circumstances by the Followers of the Apocalypse, in his words, "from the full effects of the transformation into a heinous beast". He joined as a full-fledged member shortly afterwards.
The game takes place in the year 2161 on the West Coast of what used to be the United States of America, particularly in California. It begins in Vault 13, the protagonist's home. Vault 13's water chip, a computer chip responsible for the water recycling and pumping machinery, has broken. Armed with a PIPBoy 2000 and meager equipment, the protagonist is sent out into the remains of California to find another water chip.